Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway of a target vessel. Stents are often used in the treatment of atherosclerotic stenosis and/or restenosis in blood vessels. “Stenosis” refers to a narrowing or constriction of the diameter of a bodily passage or orifice. Typically, stents are capable of being compressed, so that they can be inserted through small cavities via catheters, and then expanded to a larger diameter once they reach their target vessel. Mechanical intervention via stents has reduced the rate of restenosis; restenosis, however, is still a significant clinical problem. “Restenosis” refers to the reoccurrence of stenosis in a blood vessel or heart valve after it has been treated (as by balloon angioplasty or valvuloplasty) with apparent success. Accordingly, stents have been modified to perform not only as a mechanical scaffolding, but also to provide biological therapy.
Biological therapy can be achieved by medicating a stent, typically referred to as a drug delivery stent. Drug delivery stents provide for the local administration of a therapeutic substance at the diseased site. In contrast, systemic administration of a therapeutic substance may cause adverse or toxic side effects for the patient because large doses are needed in order for the therapeutic substance to have an efficacious effect at the diseased site. Thus, local delivery is a preferred method of treatment in that smaller total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. Local delivery therefore produces fewer side effects and achieves more favorable results.
A typical method for medicating an implantable device includes, for example, applying a composition containing a polymer, a solvent, and a therapeutic substance to the implantable device using conventional techniques, such as spray-coating or dip-coating. The method further includes removing the solvent, leaving on the implantable device surface a coating of the polymer with the therapeutic substance impregnated in the polymer.
In a typical spray-coating method, a stent is mounted on a mandrel of a spray-coating device. Generally, the stent will rest on, or contact components of, a mandrel (or the mandrel itself) which supports the stent and allows it to rotate during a spray-coating process. The contact between the portions of the mandrel and stent, however, inevitably cause coating defects. These defects can include cob-webbing, tearing, bridging, clumping and/or lack of coating on portions of the stent. The embodiments of the present invention are intended to address coating defect issues caused by conventional mandrel designs.